This study is to explore effects of nitrogen application and straw incorporation on abundance of relevant microbes and CH
4 and N2O fluxes in a midseason aerated rice paddy field. Fluxes of CH
4 and N2O were recorded, and abundance of relevant soil microbial functional genes was determined during rice‐growing season in a 6‐year‐long fertilization experiment field in China. Results indicate that application of urea significantly changed the functional microbial composition, while the influence of straw incorporation was not significant. Application of urea significantly decreased the gene abundances of archaeal amoA and mcrA, but it significantly increased the gene abundances of bacterial amoA. CH
4 emission was significantly increased by fresh straw incorporation. Incorporation of burnt straw tended to increase CH
4 emission, while the urea application had no obvious effect on CH
4 emission. N2O emission was significantly increased by urea application, while fresh or burnt straw incorporation tended to decrease N2O emission. The functional microbial composition did not change significantly over time, although the abundances of pmoA, archaeal amoA, nirS, and nosZ genes changed significantly. The change of CH
4 emission showed an inverse trend with the one of the N2O emissions over time. To some extent, the abundance of some functional genes in this study can explain CH
4 and N2O emissions. However, the correlation between CH
4 and N2O emissions and the abundance of related functional genes was not significant. Environmental factors, such as soil Eh, may be more related to CH
4 and N2O emissions.
To discover bacteria with potential biocontrol activity against the rice sheath blight (RSB) pathogen, Rhizoctonia solani, cowdung (CD) associated bacteria were screened for antifungal activity a dual-culture method. Five potential biocontrol bacteria were identified to species-level based on their colony morphology, physiology, biochemical characteristics, utilization of carbon sources, micromorphology and 16S rRNA sequences. The ability of two selected strains to inhibit RSB was evaluated in vivo and in vitro. The median effective concentration (EC 50 ) of crude extract from Streptomyces cochorusii strain NF0919 (NF0919) culture filtrate was 1.3 lg ml -1 , lower than the EC 50 of Jinggangmycin (a commercial antifungal agent widely used in China). At a concentration of 25.0 lg ml -1 , the crude extract completely inhibited mycelial growth of R. solani. The field biocontrol efficacy after spraying 7 days in 2013 and in 2014 was 78.4 and 98.1% with crude extract from NF0919 culture filtrate and 71.1 and 94.2% with fresh cells of Bacillus amyloliquefaciens strain SB177 (SB177). Results from the 2-year field experiment suggested that the crude extract from NF0919 culture filtrate or fresh cells of SB177 provided better disease control than other fungicides (Jinggangmycin and/ or Kresoxim-methyl). S. cochorusii strain NF0919 and B. amyloliquefaciens strain SB177 have good potential for field application and commercial use against the RSB pathogen.
Nowadays, there is an urgent need for the investigation of the field dissipation and assessment of the preharvest interval for trichlorfon residues on rice. To protect consumers from potential health risks, this study can provide references for the safe application of trichlorfon in the rice fields. Results of the field dissipation study showed that the dissipation dynamic equations of trichlorfon were based on the first-order reaction dynamic equations and that the dissipation rates vary among rice plant, brown rice, rice bran, soil, and water. The 2-year field trials conducted in Yangzhou and Xiaogan suggested the interval of each application for trichlorfon on rice to be at least 7 days when 80 % trichlorfon SP was sprayed with a dose ranges between 80 and 160 a.i g/667 m(2). Additionally, the preharvest interval of the last application should be at least 15 days to ensure the amounts of residues below the maximum residue limits of trichlorfon on brown rice (0.1 mg/kg).
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